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Comment by noprocrasted | Hacker News Reader

> mostly CAN

CAN is just the physical and framing layer. The data that goes over it is a whole different matter, and it's proprietary to every vendor, incompatible and generally undocumented.

For a lot of cars you can't even swap the exact same ECU between vehicles (due to bullshit like the VIN being written into it for no reason, and often no official way to change that other than "buy a new module" - so you have to hack around with reverse engineering & EEPROM programmers), let alone mix and match completely different parts.

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> the VIN being written into it for no reason

There is good reason for this: theft protection. A long known crime model is the "chop shop" where they tow away a car, then cut it up for parts. Because the VIN is in the ECU a chop shop has less incentive to exist since there is less money in it.

It does of course make legitimate repairs harder, and probably there should be a process to write a new VIN in - but it should only be available to someone who can verify the ECU wasn't stolen (which isn't free).

EEPROM programmers and various other ways of rewriting this VIN (turnkey tools using undocumented diagnostic commands giving you unauthenticated read/write access to memory) means it's just one insignificant expense for the chop shop (as it's amortized over all their cars) vs a multi-thousand-dollar investment in money for a legitimate vehicle owner or part-time mechanic.

Only if it is done via EEPROM and not via something more complex. Though your point stands.

That's true, but it's usually pretty simple to reverse engineer, and that's been done for a lot of cars. CAN message are generally sent out at fixed time intervals, and correspond to some physical or control value, with a simple linear mapping between some physical unit and the value in the message. You collect some CAN data, change something like pressing the accelerator, see what changes, record results.

Just search for "aftermarket ECU", you'll find lots of them; generally for high-performance cars that gearheads want to soup up further, but the same basic principle applies to most ECUs.

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